Memory

ABSTRACT

A memory including a memory element having a memory layer that retains information based on a magnetization state of a magnetic material, and a conductor electrically connected to the memory element is provided. In the memory, a magnetization pinned layer is provided for the memory layer through an intermediate layer, the intermediate layer is formed of an insulator, and spin-polarized electrons are injected in a stacking direction to invert a magnetization direction of the memory layer, so that information is recorded in the memory layer. The magnetic material is also provided for the conductor, so that a magnetic field with current flowing in the conductor is enhanced and a leakage magnetic field is applied to the memory layer to cause a deviation of the magnetization direction of the memory layer. Current in the stacking direction flows into the memory element through the conductor, so that spin-polarized electrons are injected.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationJP2006-143100 filed in the Japanese Patent Office on May 23, 2006, theentire contents of which is being incorporated herein by reference.

BACKGROUND

The present disclosure relates to a memory including a memory elementformed of a memory layer that stores a magnetization state of aferromagnetic layer as information and a magnetization pinned layerhaving a pinned magnetization direction, in which current is caused toflow in a direction perpendicular to a film surface to injectspin-polarized electrons, so that a magnetization direction of thememory layer is changed, and also relates to a memory including thememory element that may suitably be used as a non-volatile memory.

High-speed and high-density DRAMs have been widely used as random accessmemories in information apparatus such as computers.

However, since DRAMs are volatile memories in which information iserased when a power supply is switched off, non-volatile memories inwhich information is not erased have been desired with the power supplybeing switched off.

According to Nikkei Electronics, Feb. 12, 2001 (pp. 164-171), forexample, magnetic random access memories (MRAMs) that are configured torecord information by magnetization of a magnetic material have beenattracted attention and developed as potential non-volatile memories.

In an MRAM, current is caused to flow into two types of address wiringsalmost perpendicular to each other (word lines and bit lines),respectively, to invert magnetization of a magnetic layer of a magneticmemory element in an intersection of the address wirings based on acurrent magnetic field generated from each address wiring, so thatinformation is recorded.

A schematic view (perspective view) of a typical MRAM is shown in FIG.1.

In an area isolated by an element isolation layer 102 of a semiconductorsubstrate 110 such as a silicon substrate, a drain region 108, sourceregions 107, and gate electrodes 101 are respectively formed which formselective transistors for selecting each memory cell.

Word lines 105 extending in a longitudinal direction in the figure areprovided above the gate electrodes 101.

The drain region 108 is formed both on the left and right selectivetransistors in the figure, and a wiring 109 is connected to the drainregion 108.

Magnetic memory elements 103 each having a memory layer in which amagnetization direction is inverted are placed between the word lines105 and bit lines 106 that are placed above the word lines 105 andextend in a transverse direction in the figure. The magnetic memoryelements 103 are formed of magnetic tunnel junction elements (MTJelements), for example.

Further, the magnetic memory elements 103 are electrically connected tothe source regions 107 through a bypass line 111 in a horizontaldirection and a contact layer 104 in a vertical direction.

Current is caused to flow into the word lines 105 and the bit lines 106,respectively, to apply a current magnetic field to the magnetic memoryelements 103, so that a magnetization direction of the memory layers ofthe magnetic memory elements 103 can be inverted to record information.

In order to allow a magnetic memory such as MRAM to stably retainrecorded information, a magnetic layer (memory layer) to recordinformation preferably has a certain coercive force.

On the other hand, in order to rewrite the recorded information, acertain amount of current is preferably caused to flow into addresswirings.

As an element forming an MRAM is reduced in size, a value of currentthat inverts a magnetization direction tends to be increased. Incontrast, since address wirings are thin, it is difficult to cause asufficient amount of current to flow.

According to Japanese Patent Application Publication No. 2003-17782,U.S. Pat. No. 6,256,223, Phys. Rev. B 54.9353 (1996), and J. Magn. Mat.159.L1 (1996), for example, under these circumstances, memoriesconfigured to use magnetization inversion by spin injection have beenattracted attention as those configured to allow magnetization to beinverted using a smaller amount of current.

In magnetization inversion by spin injection, electrons spin-polarizedby passing through a magnetic material are injected into anothermagnetic material to invert magnetization in the other magneticmaterial.

For example, current is caused to flow into giant magnetoresistanceelements (GMR elements) or magnetic tunnel junction elements (MTJelements) in a direction perpendicular to a film surface of theelements, so that a magnetization direction of at least some of magneticlayers of the elements can be inverted.

Magnetization inversion by spin injection is advantageous in thatmagnetization can be inverted without increasing an amount of currenteven if an element is reduced in size.

FIGS. 2 and 3 show schematic views of a memory configured to utilize theabove-described magnetization inversion by spin injection. FIG. 2 is aperspective view, and FIG. 3 is a sectional view.

In an area isolated by an element isolation layer 52 of a semiconductorsubstrate 60 such as a silicon substrate, a drain region 58, sourceregions 57, and gate electrodes 51 that form selective transistors forselecting each memory cell are respectively formed. Of these, the gateelectrodes 51 also function as word lines extending in a longitudinaldirection in FIG. 2.

The drain region 58 is formed both on the left and right selectivetransistors in FIG. 2, and a wiring 59 is connected to the drain region58.

Memory elements 53 each having a memory layer in which a magnetizationdirection is inverted by spin injection are placed between the sourceregions 57 and bit lines 56 that are placed above the source regions 57and extend in a transverse direction in FIG. 2.

The memory elements 53 are formed of magnetic tunnel junction elements(MTJ elements), for example. Reference numerals 61 and 62 in the figuredenote magnetic layers. One of the two magnetic layers 61 and 62 is amagnetization pinned layer in which a magnetization direction is pinned,and the other is a magnetization free layer in which a magnetizationdirection is changed, specifically, a memory layer.

The memory elements 53 are connected to the bit lines 56 and the sourceregions 57 respectively through upper or lower contact layers 54. Thus,a magnetization direction of the memory layer can be inverted by spininjection by causing current to flow into the memory elements 53.

Such a memory configured to utilize magnetization inversion by spininjection has a feature in that the memory can have a device structuremore simplified as compared with a typical MRAM shown in FIG. 1, andtherefore can be a high-density memory.

The memory configured to utilize magnetization inversion by spininjection is more advantageous than a typical MRAM in whichmagnetization is inverted by an external magnetic field, because anamount of writing current is not increased even if the elements arefurther reduced in size.

In an MRAM, writing wirings (word lines and bit lines) are providedseparate from memory elements, and information is written (recorded)based on a current magnetic field generated by causing current to flowinto the writing wirings. Thus, an amount of current for writing can besufficiently caused to flow into the writing wirings.

In contrast, in a memory configured to utilize magnetization inversionby spin injection, spin injection is preferably performed by causingcurrent to flow into a memory element to invert a magnetizationdirection of a memory layer.

Since information is written (recorded) by directly causing current toflow into the memory element in this manner, the memory element isconnected to a selective transistor to form a memory cell in order toselect a memory cell in which writing is performed. In this case, anamount of current caused to flow into the memory element is limited toan amount of current which can be caused to flow into the selectivetransistor (saturation current of the selective transistor).

Therefore, writing is preferably performed using current in an amountequal to or smaller than the saturation current of the selectivetransistor, and an amount of current caused to flow into the memoryelement is preferably reduced by improving spin injection efficiency.

In order to amplify a read signal, a high magnetoresistance change ratemay preferably be obtained. To secure a high magnetoresistance changerate, it is effective to provide a memory element having an intermediatelayer in contact with both sides of the memory layer that is a tunnelinsulating layer (tunnel barrier layer).

When the tunnel insulating layer is used as an intermediate layer inthis manner, an amount of current caused to flow into the memory elementis limited in order to prevent dielectric breakdown of the tunnelinsulating layer. From this viewpoint, an amount of current during spininjection is preferably suppressed.

Typically, a memory is configured to store and retain informationwritten by current, and thus a memory layer that has stability againstthermal fluctuation (thermal stability) may be required.

A memory element utilizing magnetization inversion by spin injection hasa memory layer having a smaller volume than that of a memory layer of anMRAM of the related art. That is, the memory element tends to havedecreased thermal stability.

When the memory layer includes no secured thermal stability, an invertedmagnetization direction is inverted again by heat, thereby causing awriting error.

Therefore, thermal stability is a highly important property in thememory element utilizing magnetization inversion by spin injection.

When compared memory elements utilizing magnetization inversion by spininjection that are configured to have equal spin injection efficiency,thermal stability increases with an increase in an amount of saturationmagnetization and a volume of a memory layer, thereby consuming a largeramount of current for writing.

A thermal stability index may generally be represented by a thermalstability parameter (Δ).

The thermal stability parameter (Δ) is obtained from the followingequation:

Δ=KV/kT

K: anisotropic energy, V: volume of the memory layer, k: Boltzmannconstant, T: temperature)

Accordingly, in order for a memory element having a memory layer inwhich a magnetization direction is inverted by spin injection to be usedas a memory, an amount of current necessary for magnetization inversionmay be reduced to equal to or smaller than saturation current of atransistor by increasing spin injection efficiency, and thermalstability may be acquired to stably retain written information.

A memory layer generally has an axis of easy magnetization parallel witha magnetization direction of a magnetization pinned layer.

In a stable state, magnetization of a memory layer is parallel orantiparallel with magnetization of a magnetization pinned layer.

However, in magnetization inversion by spin injection, magnetization ofa memory element and magnetization of a magnetization pinned layerpreferably form a certain finite angle. When both magnetizations form anangle of 0° (parallel state) or 180° (antiparallel state), torque byspin injection remains still and no magnetization inversion is observed.

Magnetization of a memory layer fluctuates around an axis of easymagnetization of the memory layer and slightly deviates frommagnetization of a magnetization pinned layer, because of an influenceof thermal fluctuation. When spin injection is performed in this state,torque is generated due to a small magnetization deviation, then thedeviation is gradually increased, and finally magnetization inversionoccurs.

As described above, magnetization inversion is greatly affected by amagnetization direction of a memory layer when spin injection starts.For example, when a magnetization direction of a memory layer is almostparallel or antiparallel with a magnetization direction of amagnetization pinned layer, a long time may be consumed to invert themagnetization direction of the memory layer, and a spin injection memorymay no longer be advantageous because information cannot be recorded athigh rates.

In addition, a thermal stability parameter Δ may be increased in orderto reduce an influence of thermal fluctuation. However, this may force amagnetization direction of a memory layer to agree with a magnetizationdirection of a magnetization pinned layer directly, and thus it isdifficult to meet a demand to reduce an inversion time.

SUMMARY

According to an embodiment, there is provided a memory that can stablyrecord information at high rates.

A memory according to an embodiment includes at least a memory elementhaving a memory layer that retains information based on a magnetizationstate of a magnetic material, and a conductor electrically connected tothe memory element. The memory element includes a magnetization pinnedlayer that is provided for the memory layer through an intermediatelayer, the intermediate layer that is formed of an insulator, andspin-polarized electrons that are injected in a stacking direction toinvert a magnetization direction of the memory layer, so thatinformation is recorded in the memory layer. The magnetic material isprovided for at least part of the conductor, so that a magnetic fieldcaused with current flowing in the conductor is enhanced and a leakagemagnetic field is applied to the memory layer of the memory element tocause a deviation of the magnetization direction of the memory layer.Current in the stacking direction flows into the memory element throughthe conductor, so that spin-polarized electrons are injected.

A memory according to the above-described embodiment is configured toinclude a memory element having a memory layer that retains informationbased on a magnetization state of a magnetic material, in which amagnetization pinned layer is provided for the memory layer through anintermediate layer, the intermediate layer is formed of an insulator,and spin-polarized electrons are injected in a stacking direction tochange a magnetization direction of the memory layer, so thatinformation is recorded in the memory layer. Thus, spin-polarizedelectrons can be injected by causing current to flow in a stackingdirection to record information.

Current in the stacking direction flows into the memory element throughthe conductor electrically connected to the memory element, so thatspin-polarized electrons are injected. Thus, spin-polarized electronsare injected by causing current in the stacking direction to flow intothe memory element through the conductor, so that information can berecorded in the memory element by spin injection.

Further, the magnetic material is provided for at least part of theconductor, so that a magnetic field caused with current flowing in theconductor is enhanced and a leakage magnetic field is applied to thememory layer of the memory element to cause a deviation of amagnetization direction of the memory layer. Accordingly, amagnetization direction of the memory layer is caused to deviate (from adirection of axis of easy magnetization of the memory layer) by aleakage magnetic field from the magnetic material, so that an amount oftime used for inverting a magnetization direction of the memory layer torecord information may be reduced. Use of a memory of theabove-described embodiment of the present invention may reduce an amountof time for inverting a magnetization direction of the memory layer torecord information, and thus can record information at high rates.

Further, an amount of current for inverting magnetization can be reducedby causing magnetization of the memory layer to deviate, and hence powerconsumption for the memory can be decreased.

In addition, information can be recorded at high rates while securingsufficient thermal stability.

Accordingly, a memory capable of recording information at high rateswith high reliability can be achieved.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view schematically showing a configuration of anMRAM of the related art.

FIG. 2 is a schematic configuration diagram (perspective view) of amemory utilizing magnetization inversion by spin injection.

FIG. 3 is a sectional view of the memory of FIG. 2.

FIG. 4 is a schematic configuration diagram (perspective view) of amemory according to an embodiment.

FIG. 5 is a sectional view of a memory element of FIG. 4.

FIG. 6 is an enlarged perspective view of a main part (a vicinity ofmemory element) of a memory having a configuration of the related artwhich utilizes magnetization inversion by spin injection.

FIG. 7 is an enlarged perspective view of a main part (a vicinity ofmemory element) of the memory of FIG. 4.

FIGS. 8A and 8B are views describing an effect of a magnetic field whencurrent is caused to flow into the configuration of FIG. 7.

FIG. 9 is an enlarged perspective view of a main part (a vicinity ofmemory element) of a memory according to another embodiment.

FIGS. 10A and 10B are views describing an effect of a magnetic fieldwhen current is caused to flow into the configuration of FIG. 9.

FIG. 11 is an enlarged perspective view of a main part (a vicinity ofmemory element) of a memory according to still another embodiment.

FIGS. 12A and 12B are views describing an effect of a magnetic fieldwhen current is caused to flow into the configuration of FIG. 11.

DETAILED DESCRIPTION

An outline is illustrated below before describing the specificembodiments.

In an embodiment, information is recorded by inverting a magnetizationdirection of a memory layer of a memory element by the above-describedspin injection. The memory layer is formed of a magnetic material suchas a ferromagnetic layer and retains information based on amagnetization state (magnetization direction) of the magnetic material.

In a basic operation of inverting a magnetization direction of amagnetic layer by spin injection, current having a certain thresholdvalue (Ic) or higher is caused to flow into a memory element formed of agiant magnetoresistance element (GMR element) or magnetic tunneljunction element (MTJ element) in a direction perpendicular to a filmsurface of the memory element. Here, a polarity (direction) of currentdepends on a magnetization direction to be inverted.

Magnetization inversion does not occur when current having an absolutevalue smaller than the threshold value is caused to flow or current iscaused to flow in a short time.

A threshold value Jc of current for inverting a magnetization directionof a magnetic layer by spin injection is phenomenologically representedby the following equation 1 (see R. H. Koch et al., Phys. Rev. Lett. 920883021 (2004), for example).

$\begin{matrix}{J_{c} = {J_{c\; 0}\left( {1 + {\frac{\tau_{1}}{t}{\ln \left\lbrack \frac{\pi}{2\; \theta} \right\rbrack}}} \right)}} & 1\end{matrix}$

In the equation 1, J_(c0) is a property value determined by magneticproperties of a memory layer and provides a lower limit of an amount ofinversion current, τ₁ is time determined by an amount of saturationmagnetization and a damping constant of the memory layer and is a valueroughly in the order of nanoseconds, t is a writing time, and θ is anangle formed by magnetization of the memory layer and magnetization of amagnetization pinned layer.

As clear from the equation, an amount of inversion current Jc is rapidlyincreased when θ is zero (when magnetization of a memory layer isparallel or antiparallel with magnetization of a magnetization pinnedlayer). θ may not be necessarily a constant value, and randomly movesaround an axis of easy magnetization by influence of thermalfluctuation.

When the θ is a value approximate to zero at the start of spininjection, an amount of current caused to flow may not completemagnetization inversion of a memory layer and a writing failure erroroccurs due to consuming a long time for the inversion.

In an embodiment, a memory is configured to prevent a writing failureerror caused when θ is accidentally a value approximate to zero asdescribed above.

When current is caused to flow into a memory element through a metalconductor connected to the memory element, an annular magnetic field isgenerated around the current.

In typical magnetization inversion by spin injection, a magnetizationdirection of a memory layer is not significantly changed by the annularcurrent magnetic field.

By contrast, in an embodiment of the present invention, a ring currentmagnetic field is concentrated on a memory layer to cause magnetizationof the memory layer to slightly deviate from an axis of easymagnetization. Thus, an amount of time for inverting magnetization maybe reduced.

In an embodiment, a magnetic material is provided for a metal conductorelectrically connected to a memory element, so that a ring currentmagnetic field is enhanced and concentrated on a memory layer to causemagnetization of the memory layer to deviate from an axis of easymagnetization. The metal conductor having the magnetic material providedmay be directly connected to the memory element, or may be indirectlyconnected to the memory element through another conductor; that is, themetal conductor may be electrically connected to the memory element.

The magnetic material is provided to cover part or an entire metalconductor, for example, so that a ring current magnetic field can beenhanced and the current magnetic field can be concentrated on thememory layer.

In a configuration according to an embodiment, an amount of time usedfor inverting magnetization can be reduced, and thus information can berecorded at high rates.

Further, magnetization of the memory layer is caused to deviate toincrease θ in the equation 1, so that an amount of current for invertingthe magnetization can be reduced and hence power consumption for thememory may be decreased.

In addition, an amount of time for inverting magnetization of the memorylayer can be reduced even if a thermal stability parameter Δ is notreduced. Thus, information can be recorded at high rates while securingsufficient thermal stability.

Accordingly, a memory capable of recording information at high rates canbe realized with high reliability.

Further, in an embodiment, a magnetic tunnel junction (MTJ) element isformed using a tunnel insulating layer formed of an insulator as anon-magnetic intermediate layer between a memory layer and amagnetization pinned layer, allowing to accommodate a saturation currentvalue of a selective transistor.

This allows a magnetic tunnel junction (MTJ) element formed using atunnel insulating layer to increase a magnetoresistance change rate (MRrate) and a read signal strength as compared with a giantmagnetoresistance (GMR) element formed using a non-magnetic conductivelayer.

Magnesium oxide (MgO) is particularly used as a material for a tunnelinsulating layer, so that a magnetoresistance change rate (MR rate) canbe increased as compared with a case of using aluminum oxide that hasbeen generally used.

Spin injection efficiency generally depends on an MR rate. As the MRrate increases, the spin injection efficiency is further improved,thereby further reducing a density of magnetization inversion current.

Accordingly, magnesium oxide is used as a material for a tunnelinsulating layer as an intermediate layer and a memory layer having theabove-described configuration is used, so that an amount of writingthreshold current by spin injection can be reduced, and henceinformation can be written (recorded) using a small amount of current.In addition, writing signal strength can be increased.

Thus, an MR rate (TMR rate) is secured, so that an amount of writingthreshold current by spin injection can be reduced, and henceinformation can be written (recorded) using a small amount of current.

In addition, writing signal strength can be increased.

When a tunnel insulating layer is formed of a magnesium oxide (MgO)film, the MgO film may be preferably crystallized and may maintaincrystalline orientation in a 001 direction.

In an embodiment, an intermediate layer between a memory layer and amagnetization pinned layer may not have to be formed of magnesium oxide(tunnel insulating layer); however, may be formed with variousinsulators, dielectrics, or semiconductors such as aluminum oxide,aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, and Al—N—O.

Further, in order to achieve excellent magnetoresistance properties (MRproperties) when using magnesium oxide for an intermediate layer, anannealing temperature is preferably at 300° C. or more, and preferably340° C. to 360° C. Such an annealing temperature is higher than anannealing temperature (250° C. to 280° C.) in the case of aluminum oxidethat has been used for an intermediate layer in the related art.

Such an annealing temperature may be necessary for forming anappropriate internal structure or crystalline structure of a tunnelinsulating layer of magnesium oxide or the like.

Consequently, improved MR properties can be achieved using aheat-resistant ferromagnetic material that is resistant to annealing atsuch a high temperature for a ferromagnetic layer of a memory element.

Other configurations of a memory element may be the same as previouslyknown configurations of a memory element in which information isrecorded by spin injection.

Next, specific embodiments are described.

FIG. 4 shows a schematic configuration diagram (perspective view) of amemory according to an embodiment.

The memory has a memory element placed near an intersection of two typesof address wires (word lines and bit lines, for example) perpendicularto each other.

Specifically, in an area isolated by an element isolation layer 2 of asemiconductor substrate 10 such as a silicon substrate, a drain region8, source regions 7, and gate electrodes 1 forming selective transistorsfor selecting each memory cell are respectively formed. Of these, thegate electrodes 1 also function as one type of address wirings (wordlines, for example) extending in a longitudinal direction in the figure.

The drain region 8 is formed both on the left and right selectivetransistors in the figure, and a wiring 9 is connected to the drainregion 8.

Memory elements 3 are placed between the source regions 7 and the othertype of address wirings (bit lines, for example) 6 that are placed abovethe source regions 7 and extend in a transverse direction in the figure.The memory elements 3 each have a memory layer formed of a ferromagneticlayer in which a magnetization direction is inverted by spin injection.

The memory elements 3 are placed near an intersection of the two typesof address wirings 1 and 6.

The memory elements 3 are connected to the bit lines 6 and the sourceregions 7 respectively through upper or lower contact sections 4 and 5.

Thus, a magnetization direction of the memory layer can be inverted byspin injection by causing current to flow into the memory elements 3 ina vertical direction through the two types of address wirings 1 and 6.

FIG. 5 shows a sectional view of the memory element 3 of the memoryaccording to the present embodiment.

As shown in FIG. 5, the memory element 3 has a magnetization pinnedlayer 31 provided under a memory layer 17 in which a direction ofmagnetization M1 is inverted by spin injection. An antiferromagneticlayer 12 is provided under the magnetization pinned layer 31, and amagnetization direction of the magnetization pinned layer 31 is pinnedby the antiferromagnetic layer 12.

An insulating layer 16 is provided as a tunnel barrier layer (tunnelinsulating layer) between the memory layer 17 and the magnetizationpinned layer 31, and an MTJ element is formed of the memory layer 17 andthe magnetization pinned layer 31.

A ground layer 11 is formed under the antiferromagnetic layer 12, and acap layer 18 is formed on the memory layer 17.

The magnetization pinned layer 31 has a stacked ferrimagnetic structure.

Specifically, the magnetization pinned layer 31 includes twoferromagnetic layers 13 and 15 that are stacked andantiferromagnetically bonded through a non-magnetic layer 14.

Since the ferromagnetic layers 13 and 15 of the magnetization pinnedlayer 31 form a stacked ferromagnetic structure, magnetization M13 ofthe ferromagnetic layer 13 is right-directed and magnetization M15 ofthe ferromagnetic layer 15 is left-directed; that is, the magnetizationsare oppositely directed. Thus, magnetic fluxes leaked from theferromagnetic layers 13 and 15 of the magnetization pinned layer 31cancel each other.

A material for the ferromagnetic layers 13 and 15 of the magnetizationpinned layer 31 is not specifically limited. An alloy material formed ofone or more of iron, nickel, and cobalt may be used as such a material.The material may further contain a transition metal element such as Nb,Zr, Gd, Ta, Ti, Mo, Mn, or Cu, or a light element such as Si, B, or C.Further, the ferromagnetic layers 13 and 15 may be formed by directlystacking a plurality of films with materials differing from each other(not through a non-magnetic layer), for example, by forming stackedfilms of CoFe/NiFe/CoFe.

As a material for the non-magnetic layer 14 forming a stackedferrimagnetic structure of the magnetization pinned layer 31, ruthenium,copper, chromium, gold, silver, or the like may be used.

The memory according to the present embodiment differs from a memory ofthe related art utilizing spin injection as shown in FIGS. 2 and 3,particularly in terms of the contact sections 4 and 5 connected to thememory element 3.

FIG. 6 shows an enlarged perspective view of the vicinity of a memoryelement 53 forming a memory of the related art utilizing spin injectionas a comparative example as shown in FIGS. 2 and 3 according to anembodiment. As shown in FIG. 6, contact sections 54 are connected toupper and lower surfaces of the memory element 53, respectively, and thecontact sections 42 are formed of metal conductors.

In a configuration of FIG. 6, writing voltage is applied to the contactsections 54 on and under the memory element 53, which are selected by aselective transistor or the like, so that the writing current is causedto flow into the memory element 53 and a magnetization direction isinverted by spin injection.

Here, an amount of time for inverting magnetization relates to amagnetization direction of a memory layer of the memory element 53, asdescribed above. Exceedingly long time may be used for writing when themagnetization direction of the memory layer accidentally corresponds toa magnetization direction of a magnetization pinned layer (angle: 0° or180°).

FIG. 7 shows a perspective view of a main part of a memory cell of thememory shown in FIG. 4 (enlarged perspective view of the memory element3 and its vicinity) for comparison.

In the present embodiment, as shown in FIG. 7, the upper and lowercontact sections 4 and 5 connected to the memory element 3 arerespectively formed by covering a metal conductor 21 with a magneticmaterial 22.

As a material for the magnetic material 22, any magnetic material havinga high permeability may exhibit the same effect.

For example, a general ferromagnetic alloy containing Co, Fe, or Ni as amain component may be used. Specifically, a CoFe alloy, an NiFe alloy,or a CoNiFe alloy may be used. Such a ferromagnetic alloy may alsocontain one or more additional elements including light elements such asB, C, and N; transition metal elements such as Ti, V, Cr, Zr, Nb, Mo,Hf, Ta, and W; rare earth elements such as Gd; or noble metal elementssuch as Pt and Pd. The ferromagnetic alloy may preferably contain suchan additional element.

There are no specific limitations to a method of forming a structure ofthe contact section 4 or 5 of the present embodiment. For example, thecontact section can be formed as follows.

First, a through-hole to form the contact section is formed in asurface-covered insulating layer. For example, in the case of the memoryof FIG. 4, a through-hole is formed to reach the source region 7 and thememory element 3.

Second, a thin film of the magnetic material 22 is formed along an innerwall of the through-hole.

Third, the magnetic material 22 formed on a bottom of the through-holeis removed.

Fourth, the metal conductor 21 is formed by filling the through-holewith it, and then the metal conductor 21 remaining on the insulatinglayer is removed.

The contact section 4 or 5 having a structure in which the metalconductor 21 is covered with the magnetic material 22 can be formed inthis manner.

According to the present embodiment, current I is caused to flow intothe memory element 3 through the metal conductors 21 from up to down asshown in FIG. 8A in order to perform spin injection.

In this case, a clockwise current magnetic field 23 is generated in themagnetic materials 22 of the upper and lower contact sections 4 and 5 bythe downward current I.

A clockwise current magnetic field 23 is then generated in the memorylayer 17 of the memory element 3 as shown in FIG. 8B in a horizontalplane across the memory layer of the memory element 3 indicated by thedotted line in FIG. 8A, by a leakage magnetic field from the magneticmaterials 22 of the upper and lower contact sections 4 and 5 and thecurrent magnetic field by the downward current I.

The current magnetic field 23 can shift a direction of magnetization M1of the memory layer 17 to deviate from a direction of axis of easymagnetization (a direction of magnetization M13 or M15 of amagnetization pinned layer 31) to a direction of axis of hardmagnetization.

The magnetic materials 22 having a high permeability are provided forthe contact sections 4 and 5 in this manner, so that the currentmagnetic field 23 by the current I flowing in the metal conductors 21 isconcentrated around the magnetic materials 22. As a result, the strongmagnetic field 23 is generated around the memory layer 17, andconsequently a direction of magnetization M1 of the memory layer 17 iscaused to slightly deviate from a direction of magnetization M13 or M15of the magnetization pinned layer 31.

Here, inversion of magnetization M1 of the memory layer 17 is causedonly by spin injection, and the concentrated current magnetic field 23is used for initiating spin injection.

When current is caused to flow upward and inverse to the current I inFIG. 8A, a counter-clockwise magnetic field is generated in the memorylayer 17 by the magnetic materials 22 of the contact sections 4 and 5,and the magnetic field makes a direction of magnetization M1 of thememory layer 17 slightly deviate from a direction of magnetization M13or M15 of the magnetization pinned layer 31.

Accordingly, when a direction of magnetization M1 of the memory layer 17is inverted to any directions, the direction of magnetization M1 of thememory layer 17 can be caused to deviate with an effect of the magneticfield.

In the above-described present embodiment, the metal conductors 21 intowhich current is caused to flow are covered with the magnetic materials22 in the contact sections 4 and 5 on and under the memory element 3.Thus, the current magnetic field 23 with current flowing in the metalconductors 21 can be concentrated on the magnetic materials 22.

The current magnetic field 23 concentrated on the magnetic materials 22can be applied to the memory element 3 from the magnetic materials 22 asa leakage magnetic field 23. Thus, a direction of magnetization M1 ofthe memory layer 17 of the memory element 3 can be caused to deviatefrom a direction of magnetization M13 or M15 of the magnetization pinnedlayer 31, specifically, a direction of axis of easy magnetization tomake it easy to invert the direction of magnetization M1 of the memorylayer 17.

Consequently, an amount of time for inverting a direction ofmagnetization M1 of the memory layer 17 can be reduced, and thusinformation can be recorded at high rates.

Further, in the present embodiment, magnetization M1 of the memory layer17 is caused to deviate to increase θ in the equation 1, so that anamount of current for inverting the magnetization M1 can be reduced andhence power consumption for the memory may be decreased.

In addition, an amount of time for inverting magnetization M1 of thememory layer 17 can be reduced even if a thermal stability parameter Δis not decreased. Thus, information can be recorded at high rates whilesecuring sufficient thermal stability.

Accordingly, a memory capable of recording information at high rates canbe realized with high reliability.

In FIG. 7, the metal conductors 21 are covered with the magneticmaterials 22 in the upper and lower contact sections 4 and 5. However,the magnetic material 22 may also be provided for only one of thecontact sections.

In the above-described embodiment shown in FIGS. 4, 5, 7, and 8, themetal conductors 21 of the upper and lower contact sections 4 and 5 areon a single straight line. However, metal conductors of upper and lowercontact sections may be shifted through another metal layer such as abypass line 111 of an MRAM shown in FIG. 1. An example of this case isdescribed below.

FIG. 9 shows an enlarged perspective view of a main part (a vicinity ofmemory element) of a memory according to another embodiment.

In the present embodiment, in particular, a memory element 3 isconnected to a metal conductor 21 of a lower contact section 5 through abypass line 24 indicated by a dot-dash-line in the figure, and the metalconductors 21 of the upper and lower contact sections 4 and 5 areshifted in a transverse direction.

The upper contact section 4 has only the metal conductor 21 and does nothave a magnetic material 22. The lower contact section 5 has the metalconductor 21, right half of which is covered with the magnetic material22.

There are no specific limitations to a method of forming a structure ofthe lower contact section 5 of the present embodiment. For example, thecontact section 5 can be formed by partially modifying the formationmethod described for the previous embodiment.

For example, the magnetic material 22 may be formed on right half of athrough-hole of an insulating layer by depositing the magnetic material22 obliquely or masking left half of the through-hole. The magneticmaterial 22 may also be formed on an entire inner wall of a through-holeand then remove the magnetic material 22 formed on left half of thethrough-hole.

Alternatively, the columnar metal conductor 21 may be formed and thenthe magnetic material 22 may be deposited from the upper right to formthe magnetic material 22 on right half of the metal conductor 21.

According to the present embodiment, current I is caused to flow intothe memory element 3 through the metal conductors 21 from up to down asshown in FIG. 10A in order to perform spin injection.

In this case, a clockwise current magnetic field 23 is generated in themagnetic material 22 of the lower contact section 5 by the downwardcurrent I. Since the magnetic material 22 of the lower contact section 5is provided only for right half of the metal conductor 21, the currentmagnetic field 23 is leaked from the contact section 5 to the left.

Then, a magnetic field 23 directed from front to back is generated in amemory layer 17 of the memory element 3 as shown in FIG. 10B in ahorizontal plane across the memory layer of the memory element 3 whichis indicated by the dotted line in FIG. 10A, by the leakage magneticfield from the magnetic material 22 of the lower contact section 5.

The magnetic field 23 can shift a direction of magnetization M1 of thememory layer 17 to deviate from a direction of axis of easymagnetization (a direction of magnetization M13 or M15 of amagnetization pinned layer 31) to a direction of axis of hardmagnetization.

When current is caused to flow upward and inverse to the current I inFIG. 8A, a counter-clockwise magnetic field is generated in the memorylayer 17 by the magnetic material 22 of the lower contact section 5, andthe magnetic field shifts a direction of magnetization M1 of the memorylayer 17 to slightly deviate from a direction of magnetization M13 orM15 of the magnetization pinned layer 31.

Accordingly, when a direction of magnetization M1 of the memory layer 17is inverted to any directions, the direction of magnetization M1 of thememory layer 17 can be caused to deviate with an effect of the magneticfield.

In the above-described present embodiment, the metal conductor 21 intowhich current is caused to flow is covered with the magnetic material 22in the contact section 5 under the memory element 3. Thus, the currentmagnetic field 23 with current flowing in the metal conductor 21 can beconcentrated on the magnetic material 22.

The current magnetic field 23 concentrated on the magnetic material 22can be applied to the memory element 3 from the magnetic material 22 asa leakage magnetic field 23. Thus, a direction of magnetization M1 ofthe memory layer 17 of the memory element 3 can be caused to deviatefrom a direction of magnetization M13 or M15 of the magnetization pinnedlayer 31, specifically, a direction of axis of easy magnetization tofacilitate to invert the direction of magnetization M1 of the memorylayer 17.

Further, since the metal conductor 21 of the contact section 5 under thememory element 3 is placed to the right of the memory element 3, themagnetic field 23 can be more effectively applied to the memory layer 17by covering only a right half side of the metal conductor 21, theopposite side to the memory element 3, with the magnetic material 22.

Since a direction of magnetization M1 of the memory layer 17 can beeasily inverted, an amount of time for inverting the direction ofmagnetization M1 of the memory layer 17 may be reduced. Thus,information can be recorded at high rates.

In the present embodiment, an amount of current for invertingmagnetization M1 of the memory layer 17 can be reduced and hence powerconsumption for the memory may be decreased. Accordingly, informationcan be recorded at high rates while securing sufficient thermalstability, as in the previous embodiment.

Thus, a memory capable of recording information at high rates can berealized with high reliability.

The upper contact section 4 and the memory element 3 may be shifted andconnect the upper contact section 4 to the memory element 3 through abypass line 24. In this case, the magnetic material is provided for theupper contact section 4.

The contact section may be shifted with the memory element in anydirections. In any such case, the magnetic material may be provided fora side of the metal conductor opposite to the memory element.

FIG. 11 shows an enlarged perspective view of a main part (a vicinity ofmemory element) of a memory according to still another embodiment of thepresent invention.

In the present embodiment, a magnetic field is concentrated on a bypassline.

A memory element 3 is connected to a metal conductor 21 of a lowercontact section 5 through a bypass line 24, and the metal conductors 21of the upper and lower contact sections 4 and 5 are shifted in atransverse direction.

In the bypass line 24, three surfaces (lower surface and both sidesurfaces) other than an upper surface in contact with the memory element3 of a metal layer (metal conductor) 25 are covered with a magneticmaterial 26.

The upper and lower contact sections 4 and 5 have only the metalconductors 21 and include no magnetic material.

In such a configuration, a magnetic field generated when current flowsin the bypass line 24 is concentrated around a memory layer 17, whichfacilitates a deviation of a direction of magnetization M1 of the memorylayer 17 from a direction of magnetization M13 or M15 of a magnetizationpinned layer 31.

There are no specific limitations to a method of forming a structure ofthe bypass line 24 of the present embodiment. For example, the bypassline can be formed as follows.

First, a layer of the magnetic material 26 is formed.

Second, a groove-like concave portion in which the metal conductor 25 isto be embedded is formed in the layer of the magnetic material 26.

Third, the metal conductor 25 is formed by embedding the metal conductor25 in the groove-like concave portion.

Fourth, the magnetic material 26 in which the metal conductor 25 isembedded is patterned into the bypass line 24.

The bypass line 24 having a structure in which the metal conductor 25 iscovered with the magnetic material 26 can be formed in this manner.

According to the present embodiment, current I is caused to flow intothe memory element 3 through the metal conductors 21 from up to down asshown in FIG. 12A in order to perform spin injection.

In this case, the current I flows down in the contact sections 4 and 5;whereas the current I flows to the right in the metal layer 25 of thebypass line 24. A current magnetic field 23 is generated in the magneticmaterial 26 covering the metal layer 25 by the rightward current I.Since the magnetic material 26 covers only three surfaces (lower surfaceand both side surfaces) of the metal layer 25, the current magneticfield 23 is leaked from the bypass line 24 in an upper direction.

Then, a magnetic field 23 directed from back to front is generated inthe memory element 3 as shown in FIG. 12B in a vertical plane across thememory element 3 indicated by the dotted line in FIG. 12A, by theleakage magnetic field from the magnetic material 25 of the bypass line24.

The magnetic field 23 can shift a direction of magnetization M1 of thememory layer 17 of the memory element 3 to deviate from a direction ofaxis of easy magnetization (a direction of magnetization M13 or M15 of amagnetization pinned layer 31) to a direction of axis of hardmagnetization.

When current is caused to flow upward and inverse to the current I inFIG. 12A, leftward current is generated in the bypass line 24. Theleftward current generates a magnetic field inverse to the magneticfield 23 in FIG. 12A in the magnetic material 26 of the bypass line 24.Since the magnetic field generates a magnetic field directed from frontto back in the memory element 3, a direction of magnetization M1 of thememory layer 17 can be caused to deviate from a direction ofmagnetization M13 or M15 of the magnetization pinned layer 31.

Accordingly, when a direction of magnetization M1 of the memory layer 17is inverted to any directions, the direction of magnetization M1 of thememory layer 17 can be caused to deviate with an effect of the magneticfield.

In the above-described present embodiment, the metal conductor 25 intowhich current is caused to flow is covered with the magnetic material 26in the bypass line 24 placed under and connected to the memory element3. Thus, the current magnetic field 23 with current flowing in the metalconductor 25 can be concentrated on the magnetic material 26.

The current magnetic field 23 concentrated on the magnetic material 26can be applied to the memory element 3 from the magnetic material 26 asa leakage magnetic field 23. Thus, a direction of magnetization M1 ofthe memory layer 17 of the memory element 3 can be caused to deviatefrom a direction of magnetization M13 or M15 of the magnetization pinnedlayer 31, specifically, a direction of axis of easy magnetization tofacilitate to invert the direction of magnetization M1 of the memorylayer 17.

Consequently, an amount of time for inverting a direction ofmagnetization M1 of the memory layer 17 can be reduced, and thusinformation can be recorded at high rates.

In the present embodiment, an amount of current for invertingmagnetization M1 of the memory layer 17 can be reduced and hence powerconsumption for the memory may be decreased. Accordingly, informationcan be recorded at high rates while securing sufficient thermalstability, as in the previous embodiment. Thus, a memory capable ofrecording information at high rates can be realized with highreliability.

In each of the above-described embodiments, the metal conductors 21 and25 to supply current to the memory layer 17 are appropriately coveredwith the magnetic materials 22 and 26, respectively, so that theconcentrated magnetic field 23 is applied to the memory layer 17 toshift a direction of magnetization M1 of the memory layer to slightlydeviate from a direction of magnetization M13 or M15 of themagnetization pinned layer 31. Consequently, spin injection torque actsgreatly on the magnetization M1 of the memory layer 17, and thus thedirection of magnetization M1 of the memory layer 17 can be inverted ina short time.

It should be appreciated that an embodiment may employ not only a filmconfiguration of the memory element 3 shown in each of theabove-described embodiments but also various other film configurations.

In FIG. 5, the magnetization pinned layer 31 has a stacked ferrimagneticstructure formed of the two ferromagnetic layers 13 and 15 and thenon-magnetic layer 14. However, the magnetization pinned layer may beformed of a single ferromagnetic layer, for example.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A memory comprising: at least a memory element having a memory layerthat retains information based on a magnetization state of a magneticmaterial, and a magnetization pinned layer provided for the memory layerthrough an intermediate layer, the intermediate layer comprising aninsulator, and spin-polarized electrons are injected in a stackingdirection to invert a magnetization direction of the memory layer, sothat information is recorded in the memory layer; and a conductorelectrically connected to the memory element, wherein the magneticmaterial is provided for at least part of the conductor, so that amagnetic field caused by current flowing in the conductor is enhancedand a leakage magnetic filed is applied to the memory layer of thememory element to cause a deviation of the magnetization direction ofthe memory layer, and wherein current in the stacking direction flowsinto the memory element through the conductor, so that spin-polarizedelectrons are injected.
 2. A memory according to claim 1, wherein theconductor is placed on each of upper and lower surfaces of the memoryelement, and the magnetic material is provided to cover at least one ofthe upper and lower conductors.